JP3204711B2 - Finish annealing method for grain-oriented electrical steel sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for finish annealing a grain-oriented electrical steel sheet, and more particularly to a coil end portion on a side in contact with a coil cradle, which has been concerned when high-temperature finish annealing a grain-oriented electrical steel sheet in a coil state. This is a proposal for a technique for effectively reducing the occurrence of distortion in the.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is prepared by subjecting a hot-rolled sheet adjusted to a predetermined component composition to cold rolling once or twice with intermediate annealing, then decarburizing annealing, and then annealing separator. Is applied, dried, wound into a coil under the application of winding tension, and then subjected to high-temperature finish annealing in a predetermined atmosphere gas. The above-mentioned high-temperature finish annealing is performed for a long time in a state where the coil is placed in an annealing furnace with its winding axis being vertical, so that a side strain and a side distortion are generated at the coil end in contact with the coil cradle. A so-called distortion occurs. This tendency is particularly large in the case of a thin material having a thickness of 0.30 mm or less.

[0003] Incidentally, the distortion of the coil side edge portion is as follows.
Since the grain-oriented electrical steel sheets are used in a stacked state, they pose a major obstacle in both magnetic properties and workability. Therefore, this strained portion is usually trimmed after annealing. However, this trimming lowers the product yield, and it is necessary to reduce distortion of the coil side edge, which may occur during finish annealing, as much as possible.

Conventionally, as a measure to reduce the distortion of the coil side edge, for example, in Japanese Patent Application Laid-Open No. 55-110721, the amount of an annealing separator applied before box annealing is increased at the coil side edge. Proposes a method for reducing the deformation of the side edge. However, when the amount of the annealing separator at the coil side edge is large, the end magnetic properties are deteriorated.

In Japanese Patent Application Laid-Open No. 58-61231, a base plate made of the same material as a steel coil to be annealed is placed on a coil receiving stand, and the steel coil is placed on the base plate. A method for preventing the occurrence of distortion is proposed. In the above method, when the material to be treated is silicon steel, the material of the sole plate is Si steel.However, ferritic steel such as Si steel has a very low hot strength at high temperatures, and therefore, Since the coil end surface is easily cut into the bottom plate during annealing, distortion still occurs due to a slight difference in thermal expansion coefficient between the coil and the bottom plate.

Further, Japanese Patent Application Laid-Open No. Sho 62-56526 proposes a method in which a hoop coil wound tighter than the coil is placed between the coil and the coil receiving base. This method is also effective, but hoop coils buckle after only a few annealings, requiring frequent replacements and significantly increasing costs.

[0007] Further, in Japanese Patent Application Laid-Open No. 2-97622,
A method has been proposed to prevent the occurrence of distortion by setting the grain size of the coil end surface before annealing to 15 μm or more.
Although this method can reduce the buckling distortion of the lower end surface, it significantly deteriorates the magnetic characteristics of the coil end. Therefore, the original purpose of improving the product yield cannot be achieved.

[0008]

As described above, each of the conventional methods has had a considerable problem in practical use. The present invention advantageously overcomes the above problems, and can advantageously avoid the occurrence of distortion at the lower end of the coil, which is a concern in high-temperature annealing in a coil state, and can significantly improve the product yield. An object of the present invention is to provide a finish annealing method for grain-oriented electrical steel sheets.

[0009]

Means for Solving the Problems The inventors have conducted various experiments in order to clarify the mechanism of distortion generation at the coil edge. As a result, it has been found that the distortion at the coil edge portion is not caused only by the difference in thermal expansion between the coil and the sole plate, but that the strength at a high temperature has a great influence. In other words, for example, when Si steel is used as the base plate, since the Si steel has low high-temperature strength, the coil end surface cuts into the base plate surface, and as a result, even at a slight difference in thermal expansion from the coil, distortion occurs at the coil end Was newly found.

[0010] The present invention is based on the above findings. That is, according to the present invention, a hot-rolled directional magnetic steel sheet containing 4.0% by weight or less of Si (hereinafter simply referred to as “%”) is subjected to one or two or more cold rolling operations with an intermediate annealing, and then decarburization. After annealing, in a method for manufacturing a grain-oriented electrical steel sheet comprising a series of steps of applying high-temperature finish annealing after winding on a coil,
The high-temperature finish annealing, between the receiving coil and the coil mount, possess and and the transformation point containing C of more than 0.2 wt%, deer
Performed even steel material which does not cause contraction in transformation point in a state where the inserted as decking, is a high temperature finish annealing method of the grain-oriented electrical steel sheet, characterized in that.

First, the experimental results on which the present invention is based will be described. FIG. 1 schematically shows a typical batch type annealing furnace. In the figure, reference numeral 1 denotes a coil, 2 denotes a coil receiver, 3 denotes an inner cover, 4 denotes a base, 5 denotes an atmosphere gas supply pipe,
Reference numeral 6 denotes a sand seal at the bottom of the inner cover. Conventionally, a floor plate 7 of the same material as the coil 1, that is, Si steel having various thicknesses, is provided between the coil 1 and the coil receiving base 2.
And the coil support 2 to absorb the difference in thermal expansion. However, in this state, it was not possible to prevent the occurrence of distortion at the coil edge portion.
As described above.

Therefore, a steel type having a higher temperature and a higher strength than that of the Si steel was processed into the sole plate, and was actually inserted between the coil and the coil cradle to perform coil annealing. As a result, it was observed that the distortion of the edge portion of the coil was remarkably eliminated and the distortion was not. Therefore, when investigating the cause, it was found that the degree of distortion of the coil edge part was different due to the difference due to the composition of the steel used for the soleplate, particularly the difference in the amount of carbon.

That is, when a steel grade having a C content of 0.2% or more was used for the soleplate, the distortion at the edge portion was significantly reduced, whereas when the C content was low, the distortion hardly decreased. . This phenomenon can be understood from the relationship between the C content and the coefficient of thermal expansion shown in FIG. In other words, the coefficient of thermal expansion strongly depends on the amount of C. In particular, when the amount of C is 0.2% or more, the elongation changes slowly as shown by the solid line.
If the amount of C is small, the transformation occurs rapidly in a narrow temperature range, and the elongation changes rapidly.

Further, when the movements of the coil and the slab during the coil annealing were observed, it was found that the coil and the slab were relatively insulated even if the coefficient of thermal expansion was slightly different in the case of the coil and the slab where the coil did not easily bite. It was confirmed that it moved freely and distortion of the coil edge portion hardly occurred. However, at this time, if the C amount of the bottom plate is less than 0.2%,
The abrupt shrinkage of the soleplate was observed due to the sudden change in the coefficient of thermal expansion. If the movement is slow, the distortion received by the coil will be released at this time, but the coil will be properly distorted due to the rapid change.

On the other hand, when a sole plate having a C content of 0.2% or more is used, the relative movement between the coil and the sole plate is still observed, but the movement is very slow, and the coil releases the strain it receives. I knew I was going to do it. Therefore, in the present invention, containing C 0.2% or more, and have a transformation temperature, deer
Also , high-temperature finish annealing is performed after a steel plate that does not shrink at the transformation point is interposed between the coil and the coil cradle as a sole plate. Thereby, the distortion of the coil edge portion is extremely reduced.

[0016]

Although there is no particular limitation on the alloy element other than C as a base plate material, the addition of a large amount of an alloy element having a coefficient of thermal expansion that is significantly different from that of silicon steel is not preferable because it increases the distortion of the coil edge. Further, since steel having no α-γ transformation is not preferable from the viewpoint of high-temperature strength,
Limited to steel with transformation point. In addition, this floor plate material
Does not shrink at the transformation point, as shown in FIG.
For steel, the amount of coil distortion received from the soleplate is smaller.
This is convenient. It goes without saying that any conventionally known silicon-containing steel can be used as the material.

[0017]

[Example] 3.0% Si, 0.07% Mn, 0.015% S, 0.04% C
After hot rolling, a silicon-containing steel material having the following composition is cold-rolled twice with intermediate annealing, thereby obtaining a sheet thickness: 0.20 mm and a sheet width: 10
After forming a cold-rolled sheet of 00 mm, after decarburizing annealing in a continuous decarburizing annealing furnace, an annealing separating agent was applied, and then wound around a coil. Next, when the wound coil is placed on the coil cradle, 0.3% C steel (other components Si:
0.2%, Mn: 0.5%) and 3.0% Si steel (other components Mn:
0.065%) as a sole plate at 1180 ℃, 20
A time high temperature finish annealing was performed. FIG. 3 shows the results of examining the strain generation depth over the entire length of the obtained coil.

As is clear from the figure, the effect was much greater when the 0.3% C steel according to the present invention was used than when the 3.0% Si steel was used for the sole plate. Specifically, in the present invention, the distortion of 10 mm or more can be suppressed to 1/4 or less of the entire length, and the maximum distortion amount can be suppressed to 20 mm or less.

[0019]

As described above, according to the present invention, when the grain-oriented electrical steel sheet is subjected to high-temperature finish annealing in a coil state, the occurrence of side distortion at the coil end in contact with the coil cradle can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of a typical batch type coil annealing furnace.

FIG. 2 is a diagram showing a comparison of changes in thermal expansion due to differences in the amount of carbon.

FIG. 3 is a graph showing a comparison of the amount of strain generated at the lower end of a coil when 0.3% C steel and 3.0% Si steel are used as a sole plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coil 2 Coil receiving stand 3 Inner cover 4 Base 5 Atmospheric gas supply pipe 6 Sand seal 7 Floor plate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-56526 (JP, A) JP-A-58-61231 (JP, A) JP-A-2-97622 (JP, A) JP-A-3- 177518 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 9/46 501 C21D 8/12

Claims (1)

(57) [Claims] 1. A hot-rolled directional magnetic steel sheet containing Si: 4.0 wt% or less is subjected to cold rolling once or twice in between with annealing in between, then decarburizing annealing, and then wound around a coil. The method of manufacturing a grain-oriented electrical steel sheet comprising a series of steps of performing high-temperature finish annealing after the heat treatment, wherein the high-temperature finish annealing includes 0.2 wt% or more of C between the coil and the coil pedestal and a transformation point. Yes, and deer
Hot finish annealing method of a grain-oriented electrical steel sheet which is also performed in a state in which inserted a steel material that does not cause contraction in transformation as decking, characterized in that.